A ferroelectric memory has been drawing attention as a nonvolatile memory capable of high-speed operation. The ferroelectric memory is a memory that uses spontaneous polarization of a ferroelectric substance, and includes a capacitor type which is a combination of a transistor and a capacitor, and a transistor type which is used as a gate insulating film of a transistor.
There has been known an example that uses a ferroelectric phase of a hafnium silicate (HfSiOx) as the transistor-type ferroelectric memory. In this example, a gate insulating film is formed on a semiconductor substrate, an HfSiOx film which is a ferroelectric film is formed on the gate insulating film, and a control electrode is formed on the HfSiOx film. A voltage applied from the control electrode is then used to invert the polarization within the ferroelectric film and thereby write/erase information in memory cells. There has been a demand for improvements of memory characteristics in the transistor-type ferroelectric memories.